Osmotic diuretics (urea, glycerol, mannitol) used in treating brain edema will be infused in rats and the effectiveness of these agents to dehydrate brain will be measured using tissue density changes. The overall objective of this research is to obtain a better understanding of the mechanisms by which the osmotic diuretics remove water from the brain. This will be done by correlating the osmotic pressure changes of blood with that of brain and finding what pressure differentials are needed to remove brain water. When these parameters are known, the mode of drug use will be changed to maintain the proper osmotic pressure differential. In particular, the rate of administration and dose of the drug will be altered to achieve a more ideal osmotic pressure gradient. The effectiveness of the different modes of drug administration will be tested on rats with brain edema produced with a cold lesion.